Chrome ball for 3D reflection/light matching question...

Posts

• IRML253 Posts: 1,993Member

  May 2012 #2

  

  the point is kind of moot, let me explain:
  
  I know of one prototype true HDR digital video camera, the only other ways I can think of getting HDR video is to have a motion control setup and bracket a whole video; a beam splitter and multiple cameras with filters or different iso settings; or to forget digital, shoot on film, scan it and convert log to lin - what I'm trying to say is almost no source footage is going to be HDR unless you are a pro and you get to handle the sort of stuff I just mentioned
  
  also what really is HDR and what is LDR when you think about it? technically a HDR and an LDR image of the same scene at the same exposure should look exactly the same, the only difference being that HDR has the extra range hidden in the highlights, but the terms HDR and LDR only really describe the file formats, not how they're used, so it's subjective - a HDR image only covers the range that the photographer brackets for, so one HDR image might have less range than another, or even one HDR image might have less range than an LDR image
  
  anyway enough technobabble, all I can say is if you're doing something where you may use that extra range then definately go HDR, environment maps are a perfect example of this, if you're doing what I think you are then your source footage is only going to be used as a background plate, everything else will be done with the environment map so having the extra range will be important, lighting and reflective shaders will benefit from it hugely
  
  say if I take an LDR picture of a house, just because the sun is clipped in the image doesn't mean the house isn't being lit by its full power, so your environment map should be HDR to best match the full power in the real lighting, as long as your final output doesn't require you to dim the image, thus revealing the clipped highlights in the background, then no one will know you have an LDR element in the scene
• JMoney189 Posts: 127Member

  May 2012 #3

  

  IRML wrote: »

  all I can say is if you're doing something where you may use that extra range then definately go HDR, environment maps are a perfect example of this, if you're doing what I think you are then your source footage is only going to be used as a background plate, everything else will be done with the environment map so having the extra range will be important, lighting and reflective shaders will benefit from it hugely

  
  Thanks for the reply. Yes, my source footage is for background plate only. If I was using it for an environment map within 3dsmax, I would definitely go HDR as you mentioned no question.
  
  I'll do some more tests to see what works out the best for me. A while ago I did a test with my chrome ball inside my house near a window with vertical blinds. My plate footage showed the light coming through the blinds as white (blown out) because I was exposing for the interior only, but the HDR chrome ball image showed the blue sky in the reflection. I could adjust the HDR exposure to match my background plate, but would rather not create extra work as the HDR process is already more involved and I want the quickest workflow.
  

  say if I take an LDR picture of a house, just because the sun is clipped in the image doesn't mean the house isn't being lit by its full power, so your environment map should be HDR to best match the full power in the real lighting, as long as your final output doesn't require you to dim the image, thus revealing the clipped highlights in the background, then no one will know you have an LDR element in the scene

  
  I understand what you are saying, and makes perfect sense for lighting, but the reflection part of the process was throwing me off. I know Mental Ray can seperate (background, lightmap, and reflection HDR's), and I could adjust the exposure for each HDR copy to match properly. I'll see how my tests come out and decide if it's worth the extra effort.
  
  As a side note, the Canon t2i can film HDR video (using Magic Lantern), but there is an extra process involved (not too bad) and I really don't want to spend any more time as necessary.
  
  Thanks again,
  JMoney
• IRML253 Posts: 1,993Member

  May 2012 #4

  

  JMoney wrote: »

  A while ago I did a test with my chrome ball inside my house near a window with vertical blinds. My plate footage showed the light coming through the blinds as white (blown out) because I was exposing for the interior only, but the HDR chrome ball image showed the blue sky in the reflection. I could adjust the HDR exposure to match my background plate, but would rather not create extra work as the HDR process is already more involved and I want the quickest workflow.

  this sounds correct to me
  
  assuming your HDR image is the same exposure as the background image, the only way your reflections will match is if your object is 100% reflective, like a perfect mirror, if it's just mildly reflective then you should see the blue in the sky
  
  don't think of your HDR image as the wrong bit, the LDR image is the thing that's incorrect, but like I said earlier as long as you don't have to change the brightness of it no one will know
  
  

  JMoney wrote: »

  I understand what you are saying, and makes perfect sense for lighting, but the reflection part of the process was throwing me off. I know Mental Ray can seperate (background, lightmap, and reflection HDR's), and I could adjust the exposure for each HDR copy to match properly. I'll see how my tests come out and decide if it's worth the extra effort.

  when you say lighting you're thinking of the diffuse aspect of the surface, and when you say reflection you're thinking of the specular aspect of the surface, the thing is they're physically the same, in graphics we separate them but in real life the only difference is the way the photons spread after bouncing off the surface, if they stay tight together you get specular reflection, if they scatter you get diffuse reflection
  
  so what works for your lighting will also work for reflection
  
  

  JMoney wrote: »

  As a side note, the Canon t2i can film HDR video (using Magic Lantern), but there is an extra process involved (not too bad) and I really don't want to spend any more time as necessary.

  it's not ideal, you have to film at double the frame rate and it will alternate between bright and dim frames, which means when you try to make HDR frames out of it the result is moving objects doen't match up properly
• JMoney189 Posts: 127Member

  May 2012 #5

  

  say if I take an LDR picture of a house, just because the sun is clipped in the image doesn't mean the house isn't being lit by its full power, so your environment map should be HDR to best match the full power in the real lighting, as long as your final output doesn't require you to dim the image, thus revealing the clipped highlights in the background, then no one will know you have an LDR element in the scene

  don't think of your HDR image as the wrong bit, the LDR image is the thing that's incorrect

  when you say lighting you're thinking of the diffuse aspect of the surface, and when you say reflection you're thinking of the specular aspect of the surface, the thing is they're physically the same, in graphics we separate them but in real life the only difference is the way the photons spread after bouncing off the surface, if they stay tight together you get specular reflection, if they scatter you get diffuse reflection
  
  so what works for your lighting will also work for reflection

  
  Based on what you wrote, I think I'm starting to have a better understanding of all of this now. I'm planning on making a nice render of a Lamborghini model I made. I want to composite it onto a picture of a nearby parking lot on a sunny day. This will be a good test for me, and a chance to play with my chrome ball some more! LOL! People think I'm crazy when they see me taking pictures of a 12" chrome ball out in public. I don't even bother to explain because they won't understand.
  
  Thanks again, and I appreciate you taking the time to answer and to help me get a better understanding of the process.
  
  JMoney
  
  EDIT: There are three things I don't like about Mental Ray in 3dsmax. When using a skylight (via HDR) it only effects diffuse. The other problem is that it doesn't create proper shadows based on light intensity from the HDR. I have to create another light with shadows and try to match the lighting as best as possible. Finally, Final Gather and GI flickering during animation is a big issue and difficult to eliminate without using a ton of tricks.
  
  From what I've read (and seen) the V-Ray renderer is able to overcome these issues, or at least two of them. I might check out their free trial (if they have one) and compare to Mental Ray. Final Render is another one, but I haven't read up on that one as much.
• IRML253 Posts: 1,993Member

  May 2012 #6

  

  yeah the shadow thing you mentioned is a limitation in every app, because of the way the rays are all fired from the same 'infinite' distance it doesn't really capture their true direction as it was in the real world, so it's normal to create a separate light for the sun to get proper shadows
  
  the way I've been lighting things in max is to have a large inwards facing sphere in the scene textured with the HDR image, granted I know very little about max and it's not the way I'd do things in lightwave, the results are still correct - i.e. I get both lighting and reflections from it